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Polyclonal anti-Candida antibody improves phagocytosis and overall outcome in zebrafish model of disseminated candidiasis.

ABSTRACT: Fungal infections are a major cause of animal and plant morbidity and mortality worldwide. Effective biological therapeutics could complement current antifungal drugs, but understanding of their in vivo mechanisms has been hampered by technical barriers to intravital imaging of host-pathogen interactions. Here we characterize the fungal infection of zebrafish as a model to understand the mechanism-of-action for biological antifungal therapeutics through intravital imaging of these transparent animals. We find that non-specific human IgG enhances phagocytosis by zebrafish phagocytes in vivo. Polyclonal anti-Candida antibodies enhance containment of fungi in vivo and promote survival. Analysis suggests that early phagocytic containment is a strong prognostic indicator for overall survival. Although polyclonal anti-Candida antibodies protect against disease, this is not necessarily the case for individual monoclonal anti-Candida antibodies. Thus, the zebrafish appears to provide a useful model host for testing if a biological therapeutic promotes phagocytosis in vivo and enhances protection against candidemia.

SUBMITTER: Bergeron AC

PROVIDER: S-EPMC6700731 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Polyclonal anti-Candida antibody improves phagocytosis and overall outcome in zebrafish model of disseminated candidiasis.

Bergeron Audrey C AC Barker Sarah E SE Brothers Kimberly M KM Prasad Brinda C BC Wheeler Robert T RT

Developmental and comparative immunology 20161121

Fungal infections are a major cause of animal and plant morbidity and mortality worldwide. Effective biological therapeutics could complement current antifungal drugs, but understanding of their in vivo mechanisms has been hampered by technical barriers to intravital imaging of host-pathogen interactions. Here we characterize the fungal infection of zebrafish as a model to understand the mechanism-of-action for biological antifungal therapeutics through intravital imaging of these transparent an ...[more]

PMID: 27884707

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Project description:Disseminated candidiasis caused by the pathogen Candida albicans is a clinically important problem in hospitalized individuals and is associated with a 30 to 40% attributable mortality(6). Systemic candidiasis is normally controlled by innate immunity, and individuals with genetic defects in innate immune cell components such as phagocyte NADPH oxidase are more susceptible to candidemia(7-9). Very little is known about the dynamics of C. albicans interaction with innate immune cells in vivo. Extensive in vitro studies have established that outside of the host C. albicans germinates inside of macrophages, and is quickly destroyed by neutrophils(10-14). In vitro studies, though useful, cannot recapitulate the complex in vivo environment, which includes time-dependent dynamics of cytokine levels, extracellular matrix attachments, and intercellular contacts(10, 15-18). To probe the contribution of these factors in host-pathogen interaction, it is critical to find a model organism to visualize these aspects of infection non-invasively in a live intact host. The zebrafish larva offers a unique and versatile vertebrate host for the study of infection. For the first 30 days of development zebrafish larvae have only innate immune defenses(2, 19-21), simplifying the study of diseases such as disseminated candidiasis that are highly dependent on innate immunity. The small size and transparency of zebrafish larvae enable imaging of infection dynamics at the cellular level for both host and pathogen. Transgenic larvae with fluorescing innate immune cells can be used to identify specific cells types involved in infection(22-24). Modified anti-sense oligonucleotides (Morpholinos) can be used to knock down various immune components such as phagocyte NADPH oxidase and study the changes in response to fungal infection(5). In addition to the ethical and practical advantages of using a small lower vertebrate, the zebrafish larvae offers the unique possibility to image the pitched battle between pathogen and host both intravitally and in color. The zebrafish has been used to model infection for a number of human pathogenic bacteria, and has been instrumental in major advances in our understanding of mycobacterial infection(3, 25). However, only recently have much larger pathogens such as fungi been used to infect larva(5, 23, 26), and to date there has not been a detailed visual description of the infection methodology. Here we present our techniques for hindbrain ventricle microinjection of prim(25) zebrafish, including our modifications to previous protocols. Our findings using the larval zebrafish model for fungal infection diverge from in vitro studies and reinforce the need to examine the host-pathogen interaction in the complex environment of the host rather than the simplified system of the Petri dish(5).

Project description:Pharmacodynamic (PD) studies with triazoles in the neutropenic murine disseminated candidiasis model have been performed extensively for Candida albicans. They have consistently shown that the pharmacodynamic index most closely correlated with efficacy is the ratio of the 24-h area under the concentration-time curve (AUC) to the MIC, and a target 24-h free-drug AUC/MIC ratio near 25 is associated with 50% of maximal microbiologic efficacy. We utilized this model to investigate the pharmacodynamics of isavuconazole. Isavuconazole pharmacokinetics were linear over the dose range studied. Oral-gastric doses of 640, 160, 40, and 10 mg of prodrug/kg of body weight produced peak levels of 0.51 to 25.4 mg/liter, an elimination half-life of 1 to 5 h, and an AUC from 0 h to infinity (AUC0-∞) of 0.9 to 287 mg · h/liter. The AUC/MIC ratio was the pharmacodynamic index that correlated best with efficacy (R(2), 0.84). Pharmacodynamic target studies were performed using 4 C. albicans isolates with both a 24-h and a 96-h treatment duration. The strains were chosen to include previously characterized fluconazole-resistant strains. The mean 50% effective doses (ED50) (expressed in mg/kg of body weight/12 h) and associated 24-h free-drug AUC/MIC ratios were 89.3 ± 46.7 and 67.7 ± 35 for the 24-h treatment and 59.6 ± 22 and 33.3 ± 25.5 for the 96-h treatment. These differences were not statistically significant. Pharmacodynamic targets for two non-albicans Candida species were also explored. The mean ED50 (expressed in mg/kg/12 h) and associated 24-h free-drug AUC/MIC ratios were 31.2 and 6.2 for Candida tropicalis (n = 1) and 50.5 and 1.6 for Candida glabrata (n = 2). These PD targets were significantly different from C. albicans targets (P, 0.04). Isavuconazole PD targets for C. albicans are similar to those observed in this model with other triazoles. However, the PD targets for non-albicans Candida species were more than 10-fold lower than those for C. albicans (P, 0.04). This difference is similar to the species-specific PD relationships for the echinocandins. The lower PD targets for these species in this model will be important to consider in the analysis of clinical trial data and during the development of susceptibility breakpoints.

Dataset Information

Polyclonal anti-Candida antibody improves phagocytosis and overall outcome in zebrafish model of disseminated candidiasis.

Publications

Polyclonal anti-Candida antibody improves phagocytosis and overall outcome in zebrafish model of disseminated candidiasis.

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